Method for producing aminothiazole derivative and production intermediate

ABSTRACT

Provided is a method for selectively demethylating a 2-methoxy group. Specifically provided is a production method of a compound represented by formula (7) below through the following reactions.

This application is a divisional of U.S. application Ser. No. 11/573,409filed Jul. 10, 2013 and which is a National Stage of PCT/JP05/15259.

TECHNICAL FIELD

The present invention relates to a method for selectively demethylatinga methoxy group present at the ortho position (2-position) of anaromatic carboxylic acid, and a method for producing an aminothiazolederivative via the demethylation method.

BACKGROUND ART

It is known that compounds in which 2-hydroxybenzoic acids areamide-bonded to 2-aminothiazoles have an excellent gastroprokineticeffect and are useful as prophylactic and therapeutic agents forepigastric indefinite complaints, nausea, vomiting, heartburn, anorexia,abdominal bloating, gastro-oesophageal reflux, and the like (patentdocuments 1 to 3). Among these compounds, the compound represented byformula (7a) below:

particularly, has a high safety as well as an excellent gastroprokineticeffect and is useful as a prophylactic and therapeutic agent for theabove-described various gastroprokinetic disorders.

As a method for producing these 2-hydroxybenzoic acid amide derivatives,patent document 1 adopts a method which involves reacting a2-methoxybenzoic acid amide derivative with a demethylating reagent suchas pyridine hydrochloride to make a 2-hydroxybenzoic acid derivative.However, the demethylation reaction has been problematic to adoptindustrially because the reaction produces many side reactions, makingit difficult to selectively demethylate only a methoxy group selectivelyat the 2-position of the amide derivative.

On the other hand, patent documents 2 and 3 describe that the reactionof 2-methoxybenzoic acid amide derivatives with amines such as secondaryand tertiary amines selectively demethylates methoxy groups selectivelyat the 2-position thereof. However, the yield of the demethylationreaction of methoxy groups at the 2-position of the compounds is on theorder of 64.6 to 86% and has not yet reached a satisfactory level inview of an industrial method.

[Patent document 1]: WO96/36619

[Patent document 2]: WO98/58918

[Patent document 3]: Japanese Patent Laid-Open No. 2000-239224

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

An object of the present invention is to find a method for selectivelydemethylating the 2-methoxy group of an aromatic carboxylic acid andprovide an industrial method for producing an aminothiazole derivativeuseful as a medicine via the demethylation method.

Means for Solving the Problems

Accordingly, as a result of various studies of a method for selectivelydemethylating the 2-methoxy group of an aromatic carboxylic acid havingthe methoxy group at the 2-position thereof, the present inventor hasfound that the combination of a particular Lewis acid and a particularsolvent enables the selective demethylation of only the 2-methoxy groupof the aromatic carboxylic acid even when methoxy groups are present inthe 3-, 4-, and 5-positions thereof. The present inventor has furtherfound that when the amidation reaction of a 2-hydroxy aromaticcarboxylic acid with a 2-aminothiazole is carried out, the use of themeans involving reacting a phenyl ester of the 2-hydroxy aromaticcarboxylic acid with the 2-aminothiazole allows the reaction to proceedwith an extremely high yield.

The method of the present invention can be illustrated by the followingreaction formula.

(wherein ring A represents a benzene ring or a 6-membered aromaticheterocycle; R¹ represents a hydrogen atom, a lower alkyl group, ahalogen atom, a nitro group, an amino group, a mono-lower alkylaminogroup, or a di-lower alkylamino group; at least one of R², R³, and R⁴represents a lower alkoxy group, a lower alkoxylmethoxy group, anaralkoxy group, or an aralkoxylmethoxy group, preferably a methoxygroup, and the rest each represents a hydrogen atom, a lower alkylgroup, a halogen atom, a nitro group, an amino group, a mono-loweralkylamino group, or a di-lower alkylamino group; R⁵ represents ahydrogen atom or an electron-withdrawing group; and R⁶ represents analkyl group.)

Thus, the present invention provides a production method of a compoundof formula (2), comprising reacting a compound of formula (1) with aLewis acid selected from the group consisting of BF₃, TiCl₄, and AlCl₃in esteric, ketonic or amidic solvents, with the proviso that an alkalimetal bromide or an alkali metal iodide coexists in the case of BF₃.

The present invention also provides a production method of a compound offormula (3), comprising reacting a compound of formula (2) with a phenolderivative or a triphenyl phosphite derivative.

In addition, the present invention provides a production method of acompound of formula (5), comprising reacting a compound of formula (3)with a compound of formula (4) under heating at 150° C. or higher or inthe presence of a boric acid ester.

Further, the present invention provides a production method of acompound represented by formula (7), comprising reacting a compoundrepresented by formula (5) with N,N-diisopropylethylenediamine in thepresence of toluene.

In the above reaction formula showing the method of the presentinvention, a compound represented by formula (3) is a novel compound,and the compound is extremely important as an intermediate in the methodof the invention.

In addition, of the compounds represented by formula (5), a compoundwherein R⁶ is a methyl group, represented by formula (5a):

(wherein ring A and R¹, R², R³, and R⁴ are the same as defined above)is a novel compound, and the compound is also useful as an intermediatein the method of the invention.

It has been also found that the compound represented by formula (7a):

is converted to the hydrochloride thereof, followed by recrystallizationfrom an isopropanol aqueous solution to provide the compound representedby formula (7c):

stably and efficiently.

Effect of the Invention

According to the present invention, a phenyl ester represented byformula (3)is used as an intermediate to provide a compound representedby formula (7) useful as a gastroprokinetic agent at a high yield and ahigh purity.

BEST MODE FOR CARRYING OUT THE INVENTION

In the above reaction formula, ring A represents a benzene ring or a6-membered aromatic heterocycle. The 6-membered aromatic heterocycle ispreferably one containing one or two selected from a nitrogen atom, anoxygen atom, and a sulfur atom, and specific examples thereof include apyridine ring, a pyrimidine ring, a pyrazine ring, a oxazoline ring, anda thiazoline ring; a pyridine ring is preferable. Because theseheterocycles have a methoxy group at the ortho position relative to thecarboxyl group, for example, as in the formula (1), the ortho positionrelative to the carboxyl group or carbonyl group comprises a carbonatom. Thus, when the position of the carboxyl group or carbonyl group isdefined as the 1-position, specific examples of the heterocycle includea 3-pyridyl group, a 4-pyridyl group, a 5-pyridyl group, a 6-pyridylgroup, a 3,5-pyrimidinyl group, and a 4,6-pyrimidinyl group. Among thesegroups, a 3-pyridyl group, a 4-pyridyl group, a 5-pyridyl group, and a6-pyridyl group are preferable. Ring A is particularly preferably abenzene ring.

At least one of R², R³, and R⁴ is a lower alkoxy group, a loweralkoxylmethoxy group, an aralkoxy group, or an aralkoxylmethoxy group(preferably a methoxy group). According to the present invention, evenwhen one to three of R², R³, and R⁴ are each a lower alkoxy group, alower alkoxylmethoxy group, an aralkoxy group, or an aralkoxylmethoxygroup (preferably a methoxy group), only the methoxy group at the2-position relative to the carboxyl group is selectively demethylated.

Examples of the lower alkoxy groups represented by R², R³, and R⁴include a methoxy group, an ethoxy group, and a methylenedioxy group,and examples of the lower alkoxylmethoxy groups include amethoxylmethoxy group and an ethoxylmethoxy group. Examples of thearalkoxy groups include a benzyloxy group, a methoxybenzyloxy group, anda trityloxy group, and examples of the aralkoxylmethoxy groups include abenzyloxylmethoxy group and a methoxybenzyloxylmethoxy group.

Examples of the lower alkyl groups represented by R¹ to R⁴ include C₁₋₆alkyl groups such as, for example, a methyl group, an ethyl group, anisopropyl group, and an n-butyl group. Examples of the halogen atominclude a chlorine atom, a fluorine atom, a bromine atom, and an iodineatom; among these atoms, a chlorine atom, a fluorine atom, and a bromineatom are preferable. Examples of the mono-lower alkylamino group includemono-C₁₋₆ alkyl amino groups such as, for example, a methylamino group,an ethylamino group, and an isopropylamino group. Examples of thedi-lower alkylamino group include di-C₁₋₆ alkylamino groups such as, forexample, a dimethylamino group, a diethylamino group, and adiisopropylamino group.

R¹ to R⁴ are preferable when R¹ is a hydrogen atom; at least one of R²to R⁴ is a lower alkoxy group; and the rest of R² to R⁴ are each a loweralkoxy group, a lower alkyl group, a halogen atom, a nitro group, anamino group, a mono-lower alkylamino group, or a di-lower alkylaminogroup. R¹ to R⁴ are more preferable when R¹ and R⁴ are each a hydrogenatom; R² and R³ are each a lower alkoxy group, a lower alkyl group, ahalogen atom, a nitro group, an amino group, a mono-lower alkylaminogroup, or a di-lower alkylamino group. R¹ to R⁴ are still morepreferable when R¹ and R⁴ are each a hydrogen atom; R² and R³ are each alower alkoxy group, and particularly when R¹ and R⁴ are each a hydrogenatom; R² and R³ are each a methoxy group.

Examples of the electron-withdrawing group represented by R⁵ includehalogen atoms (for example, a fluorine atom), a nitro group, atrifluoromethyl group, a trichloromethyl group, a cyano group, an acetylgroup, a sulfonic acid group, and alkylsulfonic acid groups. Among thesegroups, a nitro group is particularly preferable.

Examples of the alkyl group represented by R⁶ include C₁₋₈ alkyl groupssuch as, for example, a methyl group, an ethyl group, a propyl group, anisopropyl group, an n-butyl group, a tert-butyl group, and a2-ethylhexyl group.

Each of the reaction processes is described below.

A compound of formula (1) is reacted with a Lewis acid selected fromBF₃, TiCl₄, and AlCl₃ in esteric, ketonic or amidic solvents, with theproviso that an alkali metal bromide or an alkali metal iodide coexistsin the case of BF₃, to selectively demethylate only the methoxy group atthe 2-position to provide a compound of formula (2) at a high yield.

BF₃, TiCl₄, and AlCl₃ may be in the form of a solvate or a hydrate; andBF₃.Et₂O, TiCl₄, AlCl₃, and AlCl₃.6H₂O are preferably used. These Lewisacids are each preferably used in an amount of 1.1- to 4-fold moles,particularly 1.1- to 3-fold moles based on a compound of formula (1) inview of a good balance between reaction selectivity and efficiency. WhenBF₃ is used, NaBr, NaI, KBr, KI, or the like coexists therewith for theproceeding of the selective demethylation reaction of the methoxy groupat the 2-position. Lewis acids other than these Lewis acids, such as,for example, Sn, Mg and Zn Lewis acids and Ti (OiPr)₄ do not cause thedemethylation reaction. The above-described alkali metal salt ispreferably used in an amount equimolar to that of the Lewis acid.

The reaction solvent is esteric, ketonic, or amidic solvents. The use ofa hydrocarbonic solvent such as toluene does not selectively provide acompound of formula (2) because it also demethylates a methoxy groupother than the methoxy group at the 2-position. Examples of the estericsolvent include ethyl acetate, methyl acetate, butyl acetate, andisobutyl acetate; ethyl acetate is preferable. Examples of the ketonicsolvent include acetone, 2-butanone, cyclohexanone, and cyclopentanone.Examples of the amidic solvent include dimethylformamide anddimethylacetamide; dimethylformamide is preferable. In this respect, inaddition to these solvents, other toluenic solvents may be also used.

The reaction is preferably carried out at 50 to 150° C. for 0.5 to 5hours, particularly at 60 to 80° C. for 1 to 3 hours.

According to the present invention, only the methoxy group at the2-position is selectively demethylated to provide a compound of formula(2) at a high yield of 90% or more.

A compound of formula (2) is reacted with a phenol derivative or atriphenyl phosphite derivative to provide a compound of formula (3).When the phenol derivative is used as a phenylation agent, the reactionis preferably performed in the presence of thionyl chloride, phosphorusoxychloride, or the like. When the triphenyl phosphite derivative isused as a phenylation agent, the reaction is preferably conducted in thepresence of sulfuric acid, methansulfonic acid, toluenesulfonic acid,trifluoromethanesulfonic acid, or the like. Examples of the phenolderivative include phenol and para-nitrophenol. Examples of thetriphenyl phosphite derivative include triphenyl phosphite andtri-para-nitrophenyl phosphite; triphenyl phosphite is preferable.

The phenylation reaction is preferably carried out in a hydrocarbonicsolvent such as toluene, xylene, and tetralin at room temperature to150° C. for 1 to 24 hours, particularly at 90 to 120° C. for 2 to 5hours.

A compound of formula (3) is reacted with a compound of formula (4)under heating at 150° C. or higher or in the presence of a boric acidester to provide a compound of formula (5) at an extremely high yield.

When a compound of formula (3) is reacted with a compound of formula (4)under heating at 150° C. or higher, the solvent is preferably tetralin,xylene, dimethylformamide, dimethylacetamide, or dimethylsulfoxide. Areaction temperature of lower than 150° C. prolongs the reaction time.Preferred reaction temperature is 150° C. or higher, particularly 150 to180° C. The reaction terminates in 2 to 5 hours. This method allows acompound of formula (4) with a high purity to be obtained at a highyield because it does not cause side reactions despite the high reactiontemperature.

The boric acid ester is preferably triphenyl borate. The use oftriphenyl borate allows a compound of formula (4) with a high purity tobe obtained at a high yield because it causes little side reactions. Thereaction solvent is preferably toluene or xylene. The reaction ispreferably conducted at 80 to 120° C., and terminates in 1 to 5 hoursunder this condition.

A compound of formula (5) is reacted with N,N-diisopropylethylenediamine(6) in the presence of toluene to provide a compound of formula (7).

This reaction is carried out in toluene to cause little coloration ofthe reaction solution. As a result, a compound of formula (7) obtaineddoes not become colored, simplifying the after-treatment thereof. Theuse of xylene or tetralin as a solvent tends to allow the reactionsolution to become brownish yellow. This reaction is preferablyperformed at 50 to 150° C. for 1 to 24 hours, particularly at 90 to 120°C. for 5 to 10 hours.

A production method of the compound of formula (7c) from the compound offormula (7a) is then described. The compound of formula (7a) can bepresent in the form of various acid addition salts; however, thehydrochloride thereof is preferable. The hydrochloride is present in theform of an anhydride, a monohydrate, and a trihydrate; among these, thetrihydrate thereof is excellent particularly in storage stability. Thecompound of formula (7a) is recrystallized from an isopropanol aqueoussolution to provide the trihydrate thereof (7c) stably and efficiently.The isopropanol aqueous solution used preferably has a concentration of10 to 90%. The compound of formula (7c) obtained using the isopropanolaqueous solution is stable to humidity changes, handling at roomtemperature, and formulation, and useful as a pharmaceutical rawmaterial.

EXAMPLES

Then, the present invention is described in further detail withreference to Examples. However, the present invention is not intended tobe limited thereto.

Example 1 Synthesis of 2-hydroxy-4,5-dimethoxybenzoic acid (2a)

(1) In 10 g of ethyl acetate were suspended 2.0 g of2,4,5-trimethoxybenzoic acid (1a) and 1.45 g of NaBr in a stream ofargon, to which 4.0 g of BF₃.Et₂O was then added dropwise at 25° C.,followed by heat stirring at 40° C. for 3 hours. The reaction mixturewas cooled with ice, to which 10 mL of water was then added dropwise at10° C., followed by dropwise adding 7.5 g of a 25% (w/w) sodiumhydroxide aqueous solution. Thereto was further added 10 mL of waterbefore stirring, followed by filtering off insoluble inorganic matter.To the separated aqueous layer was dropwise added 3.94 g of 35%hydrochloric acid, followed by stirring for 10 minutes. The precipitatedcrystal was collected by filtration and washed with water. The resultantcrystal was then dried under reduced pressure at 60° C. to provide 1.7 gof 2-hydroxy-4,5-dimethoxybenzoic acid (2a) at a yield of 91%.

¹H-NMR(DMSO-d₆, δ):3.71 (s,3H), 3.81 (s,3H), 6.56 (s, 1H), 7.17 (s,1H),11.15-11.30 (bs, 1H), 13.45-13.70 (bs, 1H)

(2) In 30 mL of ethyl acetate was suspended 10 g of the compound (1a) ina stream of argon, to which 6.2 mL of TiCl₄ was then added dropwise at10 to 15° C. under cooling with ice. The reaction mixture was heated toreflux, and stirred for 5 hours. This reaction mixture was cooled, towhich 4.9 g of 35% hydrochloric acid was then added dropwise at 24° C.before adding 30 mL of water, followed by heat stirring at 55° C. forone hour. The precipitated crystal was collected by filtration andwashed with water to provide 12.45 g of compound (2a) in the form of awet crystal. The moiety (6.23 g) of the resultant wet crystal wassuspended in 15 mL of water, to which 3.52 g of a 25% (w/w) sodiumhydroxide aqueous solution was then added dropwise at 18° C., followedby heat stirring at 60° C. for one hour. To the reaction mixture wasadded 20 mL of ethyl acetate, which was then subjected toliquid-separating operation, followed by dropwise adding 2.19 g of 35%hydrochloric acid to the separated aqueous layer. The precipitatedcrystal was collected by filtration and washed with water. The resultantcrystal was dried under reduced pressure at 60° C. to provide 4.13 g ofcompound (2a) at a yield of 88%.

(3) In 11 mL of dimethylformamide (DMF) were suspended 2.12 g ofcompound (1a), 4.82 g of AlCl₃.6H₂O, and 2.06 g of NaBr in a stream ofargon, which was then heat stirred at 100° C. for 5 hours. The reactionmixture was allowed to stand to cool, to which 10.4 g of 35%hydrochloric acid was then added dropwise before adding 11 mL of water,followed by heat stirring at 70° C. for one hour. The precipitatedcrystal was collected by filtration and washed with water. The resultantcrystal was dried under reduced pressure at 60° C. to provide 1.45 g ofcompound (2a) at a yield of 73%.

(4) In 20 g of toluene was suspended 6.28 g of AlCl₃ in a stream ofargon, to which 20 g of DMF was then added dropwise at 26° C. beforeadding 10.0 g of compound (1a), followed by heat stirring at 85° C. for1.5 hours. The reaction mixture was cooled, to which 5.89 g of 35%hydrochloric acid was then added dropwise before adding 17.0 g of water,followed by heat stirring at 75° C. for one hour. The precipitatedcrystal was collected by filtration and washed with water. The resultantcrystal was dried under reduced pressure at 60° C. to provide 9.0 g ofcompound (2a) at a yield of 96%.

Comparative Example 1

(1) To 1 mL of ethyl acetate were added 200 mg of compound (1a) and 387μL of BF₃.Et₂O in a stream of argon, which was then stirred at 25° C.for 5 hours. However, the reaction did not proceed under theseconditions. The reaction also did not proceed at all even underconditions of 50° C. for 5 hours using acetonitrile as a solvent. Thus,it has been found that the use of BF₃.Et₂O requires a reagent such asNaBr.

(2) In 5.0 g of toluene was suspended 500 mg of compound (1a) in astream of argon, to which 1.27 g of TiCl₄ was then added dropwise at 22°C. The reaction mixture was stirred at 70 to 75° C. for one hour.

This reaction also demethylates methoxy groups other than the methoxygroup at the 2-position, not enabling the desired compound to beselectively obtained.

(3) In 10 mL of toluene was suspended 500 mg of 2,4,5-trimethoxybenzoicacid in a stream of argon, to which 1.26 g of AlCl₃ was then added understirring at room temperature. The reaction mixture was stirred at 90 to98° C. for 2 hours.

This reaction also demethylates methoxy groups other than the methoxygroup at the 2-position, not enabling the desired compound to beselectively obtained.

From the above (2) and (3), it has been found that the combination ofBF₃.Et₂O, TiCl₄, or AlCl₃ and an esteric, ketonic or amidic solvent isimportant for selective demethylation of the methoxy group at the2-position.

Example 2 Synthesis of phenyl 2-hydroxy-4,5-dimethoxybenzoate (3a)

(1) In 10 g of xylene were suspended 1.0 g of compound (2a) and 522 mgof phenol, to which 460 μL of SOCl₂ was then added dropwise beforeheating to reflux for 3 hours, followed by further adding 184 μL ofSOCl₂ and additionally heating to reflux for one hour. The reactionsolvent was distilled off, followed by adding methanol to the residuebefore stirring. The precipitated crystal was collected by filtration toprovide 880 mg of phenyl 2-hydroxy-4,5-dimethoxybenzoate (3a) at a yieldof 64%.

¹H-NMR(DMSO-d₆, δ):3.77(s,3H),3.86(s,3H),6.66(s,1H),7.29-7.35(m,3H),7.40(s,1H),7.46-7.50(m,2H),10.29(s,1H)

(2) In 1.5 g of toluene were mixed 2.35 g of P(OPh)₃, 1.5 g of compound(2a), and 40.3 μL of H₂SO₄ in a stream of argon, followed by heating thereaction mixture to reflux before stirring for 2.5 hours. The reactionmixture was allowed to stand to cool, to which 5 g of methanol was thenadded before stirring for 30 minutes, followed by adding 2.5 g of waterand stirring for 30 minutes. The precipitated crystal was collected byfiltration and dried under reduced pressure to provide 2.0 g of phenyl2-hydroxy-4,5-dimethoxybenzoate (3a) at a yield of 96%.

Example 3 Synthesis of2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1,3-thiazole-4-carboxylic acidmethyl ester (5a)

(1) In 25 g of toluene were suspended 5.0 g of phenyl2-hydroxy-4,5-dimethoxybenzoate (3a), 3.75 g of methyl2-amino-1,3-thiazole-4-carboxylate (4a), and 5.49 g of (PhO)₃B in astream of argon, which was then stirred at 100° C. for 3 hours. Theretowas dropwise added 25 g of methanol at 70° C., followed by heating toreflux for one hour. The reaction mixture was allowed to stand to coolbefore stirring at 30° C. or lower for one hour, followed by collectingthe precipitated crystal by filtration. The crystal was dried underreduced pressure at 60° C. to provide 6.49 g of the monomethanolate ofthe title compound (5a) at a yield of 96% . The monomethanolate of thetitle compound (5a) had an extremely high purity of 99.78% as determinedby HPLC.

¹H-NMR(DMSO-d₆,δ):3.19(s,3H),3.79(s,3H),3.83(s,3H),3.84(s,3H),4.05-4.15(bs,1H),6.61(s,1H),7.63(s,1H),8.13(s,1H),11.77(s,1H),12.40(s,1H)

The drying under reduced pressure was further carried out at 100° C. toprovide the title compound (5a).

¹H-NMR(DMSO-d₆,δ):3.79(s,3H),3.83(s,3H),3.84(s,3H),6.61(s,1H),7.63(s,1H),8.13(s,1H),11.77(s,1H),12.40(s,1H)

(2) In 500 mg of tetralin were suspended 500 mg of phenyl2-hydroxy-4,5-dimethoxybenzoate (3a) and 433 mg of methyl2-amino-1,3-thiazole-4-carboxylate (4a) in a stream of argon, which wasstirred at 175° C. for 3 hours. After cooling, methanol was addedthereto, followed by stirring for one hour. The precipitated crystal wascollected by filtration and dried under reduced pressure at 60° C. toprovide 620 mg of the monomethanolate of the title compound (5a) at ayield of 92%.

Example 4 Synthesis of2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1,3-thiazole-4-carboxylic acidmethyl ester (5a)

(1) In 2.5 g of xylene were suspended 500 mg of phenyl2-hydroxy-4,5-dimethoxybenzoate (3a), 288 mg of methyl2-amino-1,3-thiazole-4-carboxylate (4a), and 204 μL of (MeO)₃B in astream of argon, which was then heated to reflux (at 140° C.) for 3hours. The reaction mixture was allowed to stand to cool, to which 5 gof methanol was then added dropwise, followed by heating to reflux forone hour. The reaction mixture was cooled with ice and then stirred forone hour, followed by collecting the precipitated crystal by filtration.The crystal was dried under reduced pressure at 80° C. for one hour toprovide 505 mg of the monomethanolate of the title compound (5a) at ayield of 80%.

(2) The reaction was carried out as described in (1), using xylene (140°C.) or tetralin (175° C.) as a solvent and employing (PhO)₃B in place of(MeO)₃B, to provide the monomethanolate of the title compound (5a) at ayield of 85% or 67%, respectively.

The results of (1) and (2) show that the reaction is preferablyconducted at 80 to 120° C., in the presence of (PhO)₃B.

Comparative Example 3

In 250 mg of xylene were suspended 250 mg of phenyl2-hydroxy-4,5-dimethoxybenzoate (3a) and 144 mg of methyl2-amino-1,3-thiazole-4-carboxylate (4a) in a stream of argon, which wasthen heated to reflux (at 140° C.) for 7 hours. The reaction was notcompleted. After cooling, methanol was added, followed by stirring forone hour. The precipitated crystal was collected by filtration and driedunder reduced pressure at 60° C. to provide 170 mg of the same compound(5a) as that of Example 4 at a yield of 55%.

The results of Comparative Example 3 and Example 3(3) show that thereaction of compound (3a) and compound (4a) by heating is preferablyperformed at 150° C. or higher.

Example 5 Synthesis of 2-hydroxy-4,5-dimethoxybenzoic acid 4-nitrophenylester (3a)

In 5.0 g of toluene were mixed 2.2 g of tris(4-nitrophenyl)phosphite,1.0 g of 2-hydroxy-4,5-dimethoxybenzoic acid, and 11 μl of H₂SO₄ in astream of argon, followed by heating the reaction mixture to refluxbefore stirring for 2 hours. The reaction mixture was allowed to standto cool, to which 5 mL of methanol was then added at 40° C. beforestirring for 30 minutes, followed by collecting the precipitated crystalby filtration before drying under reduced pressure to provide the titlecompound (3a) at a yield of 60%.

¹H-NMR(CDCl₃,δ):3.91(s,3H),3.96(s,3H),6.55(s,1H),7.37(s,1H),7.42(d,2H,J=9.0Hz),8.35(d,2H,J=9.0Hz),10.26(s,1H)

Example 6 Synthesis of2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1,3-thiazole-4-carboxylic acidmethyl ester (5a)

In 1 mL of xylene were suspended 200 mg of2-hydroxy-4,5-dimethoxybenzoic acid 4-nitrophenyl ester and 119 mg of2-amino-1,3-thiazole-4-carboxylic acid methyl ester in a stream ofargon, which was then stirred at 130° C. for 12 hours. The reactionmixture was allowed to stand to cool, to which 1 mL of methanol was thenadded, followed by heating to reflux for one hour. The resultantreaction mixture was allowed to stand to cool, followed by collectingthe precipitated crystal by filtration at 30° C. or lower before dryingunder reduced pressure to provide 180 mg of the title compound (5a) at ayield of 80%.

Example 7 Synthesis of N-[2-(diisopropylamino)ethyl]-2-[(2-hydroxy-4,5-dimethoxybenzoyl)amino]-1,3-thiazole-4-carboxamide(compound 7a)

In 30 mL of toluene was suspended 10.81 g of compound (5a) obtained inExample 4, to which diisopropylethylenediamine (6) was then addeddropwise at 70° C. in a stream of argon, followed by heat stirring at100° C. for 5 hours. The reaction mixture was allowed to stand to cool,to which 20 mL of a 10% (w/w) sodium chloride aqueous solution was thenadded at 75° C. for performing extraction operation. This operation wasrepeated once again. After removing the aqueous layer, toluene wasremoved under reduced pressure, followed by diluting the residue with 38mL of 80% (v/v) aqueous 2-propanol. Thereto was dropwise added 9.22 g of35% hydrochloric acid to precipitate the hydrochloride of compound (7a).The precipitated crystal was collected by filtration and washed with2-propanol, and then dried under reduced pressure at 50° C. to provide14.45 g of the hydrochloride of compound (7a) at a yield of 97%.

¹H-NMR(DMSO-d₆, δ):1.32 (d, 6H, J=6.4Hz), 1.35 (d, 6H, J=6.4Hz), 3.16-3.19 (m,2H),3.59-3.67 (m,4H),3.78 (s,3H), 3.82 (s,3H), 6.89 (s, 1H),7.50 (s, 1H), 7.91 (s, 1H), 8.74 (t,1H,J=5.9Hz),9.70(s, 1H), 11.80 (s,1H), 12.05-12.15 (bs, 1H)

Comparative Example 5

The reaction was carried out in the same way as that in Example 7 exceptfor the use of xylene or tetralin as a solvent. As a result, the use ofxylene or tetralin tended to allow the reaction liquid to be coloredbrownish yellow although the use of toluene made the liquid colorless orpale yellow.

Example 8 Synthesis of Compound (7)

In 8 mL of aqueous 20% 2-propanol solutin was suspended 2.0 g ofcompound (7a), which was then heat stirred for complete dissolution. Theresultant solution was allowed to stand to cool while continuing thestirring, followed by collecting, by filtration, the crystalprecipitated at an internal temperature of 20° C. before washing withaqueous 20% 2-propanol solution. The crystal was dried under reducedpressure at 50° C. to provide 1.8 g of compound (7c) at a yield of 90%.

The resultant crystal (HCl.3H₂O) had a value of 9.99 to 10.06%, comparedto a theoretical value of 9.98%, in the measurement of the water contentusing the Karl Fischer method, suggesting that it is a trihydrate. Thecompound was stable without exhibiting any change in quality due totemperature change and handling at room temperature.

The invention claimed is:
 1. A compound represented by formula (3):

wherein ring A represents a benzene ring or a 6-membered aromaticheterocycle; R1 represents a hydrogen atom; R2 and R3 each represent amethoxy group; R4 represents a hydrogen atom; and R5 represents ahydrogen atom or an electron-withdrawing group selected from a halogenatom, a nitro group, a trifluoromethyl group, a trichloromethyl group, acyano group, an acetyl group, a sulfonic acid group, and analkylsulfonic acid group.
 2. The compound of claim 1, wherein ring Arepresents a benzene ring.
 3. The compound of claim 1, wherein ring Arepresents a 6-membered aromatic heterocycle.
 4. The compound of claim1, wherein R₅ is a hydrogen atom.
 5. The compound of claim 1, wherein R₅is an electron-withdrawing group.